1. Field of the Invention
The present invention relates to a transmission, and more particularly, to a structure for mounting an output gear and a bearing to a hydraulic automatic transmission of a motor vehicle.
2. Description of the Related Art
A hydraulic automatic transmission for a motor vehicle is generally equipped with a transmission mechanism which comprises a planetary gear unit including rotating elements for transmitting engine torque, such as sun gears and planetary carriers, and hydraulic frictional engaging elements such as hydraulic wet multi-disc clutches and band brakes. In this type of hydraulic automatic transmission, supply and discharge of operating oil to and from the hydraulic frictional engaging elements are controlled to change the operating conditions of the individual rotating elements in the planetary gear unit between rotating condition and fixed condition, so that the path of transmission of the engine torque within the planetary gear unit may be changed to achieve a desired speed (transmission gear ratio). The output torque of the planetary gear unit is transmitted to driving wheels of the vehicle through an output gear coupled to the planetary gear unit, a transfer gear meshed with the output gear, and a differential coupled to the transfer gear.
Hydraulic automatic transmissions include a type wherein the output gear is located substantially in the middle of the transmission. In this type of automatic transmission, the output gear is rotatably supported via a bearing by a partition wall formed integrally with a transmission casing and is located on one side of the partition wall opposite to the planetary gear unit in the axial direction of the transmission, as disclosed in Unexamined Japanese Patent Publication (KOKAI) No. 1-98736, for example. The bearing has an outer race spline-fitted into an axial hole of the partition wall and is inseparably fixed to the partition wall by a snap ring. However, this output gear-and-bearing mounting structure in which the output gear is mounted to the partition wall of the transmission casing through the bearing fixed to the partition wall by spline-fitting and the snap ring is disadvantageous in that it is poor in strength because large torque is transmitted through the output gear.
Therefore, it can be considered to employ an output gear-and-bearing mounting structure in which the outer race of the bearing is fastened to the partition wall by bolts to thereby increase the strength. In this mounting structure, the bearing is bolted to the partition wall from the side of the partition wall opposite to the output gear in the axial direction of the transmission so that the bolts may not interfere with the output gear. This means that the bolts are located on the same side of the partition wall as the planetary gear unit with respect to the axial direction of the transmission. Thus, when using this output gear-and-bearing mounting structure for a hydraulic automatic transmission having a construction such that an actuator for supplying and discharging operating oil to and from a hydraulic frictional engaging element of the planetary gear unit has a cylinder thereof formed by part of the partition wall, the cylinder must inevitably be located more outward than the bolts in the diametrical direction of the transmission.
This arrangement results in increased diameter of the transmission, making it difficult to provide a compact transmission. Further, this output gear-and-bearing mounting structure does not permit the output gear and the bearing to be assembled into a unit beforehand, thus lowering the efficiency in assembling the output gear and its peripheral parts.